1. Field of the Invention
This invention relates to polymer compositions which include additives to increase the dielectric heating efficiency of said composition. In particular, the compositions of this invention include a polymer, e.g. a polymer substantially comprised of non-polar monomers, and an additive comprising a particulate, layered compound of a tetravalent atom and a pentavalent atom, selected from Group V of the Periodic Table of the Elements, and having an atomic weight of at least 30. The particulate, layered compounds may include organo radicals, to thereby enhance the compatibility of the particulate, layered compound and the polymer. In one aspect of this invention, the polymer compositions are thermoplastic molding compositions. In another aspect of this invention a method for molding thermoplastic molding compositions using microwave energy, in the radio frequency (RF) range of the microwave spectrum, is disclosed and claimed. In still another aspect of the invention thermoplastic molding compositions are sensitized so that energy of the microwave RF frequency can be used in the molding process. In yet another aspect the invention relates to objects molded of thermoplastic molding compositions.
2. Description of the Art
It is known that microwave RF energy may be used to increase the temperature of polymer compositions comprising polar comonomers so that the temperature is raised above the softening point and molding and other thermoplastic shaping processes are possible. However, when the polymer is not comprised of polar comonomers, i.e. copolymers comprising nonpolar comonomers, polar additives must be incorporated therein to provide sensitivity to microwave RF energy. In general, polar compounds are substantially incompatible with the nonpolar hydrocarbon polymers such as polyethylene, polystyrene, polypropylene, etc. Providing microwave sensitivity e.g. RF sensitivity, to nonpolar polymers, in view of the incompatibility of nonpolar polymers, especially hydrocarbon polymers and polar additives, is thus a problem that has been sought to be solved. One solution to this problem has been the incorporation of asbestos in certain nonpolar polymers. Asbestos, however, is difficult to finely divide to the extent that it is uniformly dispersed throughout the polymer composition. In addition, asbestos is a material which has been associated with known health problems and thus it is not used in any application where it can be conveniently replaced. A clay-based product, sold under the Frequon.RTM. trademark, has been suggested as a substitute for asbestos. (Frequon.RTM. is marketed by Phillips Petroleum Company.) This material, while not having the health-related problems of asbestos does not have sufficient heat stability at temperatures greater than 350.degree. F.
Thus, it would be desirable to have an additive which is compatible with nonpolar polymers and able to provide microwave, e.g. RF, sensitization to polymeric composites of the nonpolar polymer and the additive. It would also be desirable to have an additive which increases the dielectric heating efficiency across a relatively wide band of microwave radiation.